Thin film transistor (TFT) has been employed for driving an active matrix liquid crystal display (AMLCD) generally, but accumulation of static electricity is usually produced in fabricating thin film transistors because a glass substrate used for display is an insulator, and electro-static accumulation issues easily result in device damage and greatly reduce product yield.
Static electricity is usually generated from the process environment in thin film transistor fabrication, such as in the chemical vapor phase deposition (CVD), sputtering or plasma dry etching process. In addition, static electricity accumulation is also produced from outside conditions in process transition or substrate transmission. Static electricity accumulation cannot be cancelled by the insulating glass substrate, and an apparent potential difference is therefore induced between devices and conductors on the substrate. Once electro-static discharge (ESD) occurs, a transient high current and a transient high voltage are produced and lead to lower reliability and even perpetual damage in devices or circuits.
For ESD issues, a method of decreasing or removing static electricity sources is generally used to reduce probability of static electricity production, but static electricity production is merely restricted by controlling static electricity sources, and static electricity production cannot be completely avoided completely. If static electricity accumulates, ESD issues are still not resolved in practice. Another method of changing the driver circuit design in devices is thus utilized for resolving ESD issues, and circuit design with ESD protection is used to disperse static electricity accumulation in devices and reduce potential differences resulting from static electricity accumulation. ESD occurrence is thus eliminated greatly, and device protection is also achieved.
General circuit design with ESD protection suited to flat panel display comprises resistors type, shorting-ring type, shorting-bar type or metal lines increase. But there are drawbacks of resolution loss and aperture ratio reduction in the circuit design types aforementioned, and shorting-rings or shorting-bars are thus located in peripheral circuit regions in panels to prevent display region from being affected. However, static electricity released by peripheral shorting-ring or shorting-bar design is limited, and more particularly, ESD in a TFT or a pixel is particularly unavoidable.